Arizona weekly enterprise., 1887-07-09
IRON GENERALIZATION.
How 1t Produces Changes in the Fibers O
 the Metals and weakens it.


 Der night seven years ago, carrying ev- cry living soul upon it to certain death, there has beenno railroad bridge dis aster that has excited so much public attention as that which occurred on the Boston & Providence railroad at the Bussey bridge near Boston. In both the cause appears to have been structural defect. This may also be said of the Ashtabula accident, whose horrors, how ever, were increased by the fierce work of flames and the inclemencies of 8 bit terlY cold winter night.
 Bridge accidents are considered by all railroad men as incomparably the worst to which travel by rail is exposed, and as among the most difficult to guard against absolutely. One source of danger was shown when the peculiar effects of a locomotives hammer blows upon a track were explained. The theory was advanced that a girder of the bridge had broken beneath the en- gine's drivers, whose pounding upon the effectively constructed bridge was thus primarily the cause of the acci- dent. This brings up a phase of rail road and bridge accidents which is at present receiving great deal of atten- tion. Disqualification in the material of iron bridges is an element of danger now so we'll recognized that the Penn sylvania Railroad Company has adopted the definite policy of Substituting stone for iron bridges, and the same plan is being followed by other railroad com panies.
 The lifetime of an iron bridge is from twenty to twenty-five years, and con- stant care is necessary to insure its safety. The Ashtabula bridge was thirteen years old, and at the time it fell beneath the weight of two engines and a heavy express train the theory was commonly advanced that crystal ization had impaired its original strength. The two great moving causes of specialization are vibration and the hammer blows of the locomotive, which gradually, by repeated impact, turn the fiber of iron or steel into a mass of crystals, needing only some unusual pressure or blow to cause them to break apart. Add to this the oscillation caused by the passage of trains at a high rate of speed, and it will be seen that an iron bridge is exposed to pecu- liar perils, which can only be guarded against by rigid inspection and con- stant renewals.
 Specialization was one of several theories advanced by Park Benjamin, a New York engineer, to account for the Fay bridge accident. He said:
 General indications go to show that the cause must be sought in an abnormal condition of the structure, orrather one which did not enter into the calculations of the builders. Such a condition would be the deterioration of the metal by it's change from a fibrous to a crystalline state under repeated vibration. That this occurs in railway bridges has been vigorously disputed by many we'll nknown engineers. On the other hand, ymany examples are quoted by different authorities to support the theory.-AP- f|propos to this particular accident, a distinguished French engineer and iron founder now in this country informs us that he has known bars of iron made by himself from Scotch pig to change from a tough fbrous to a brittle crystalline structure in travelling by rail only from the north of France to Paris. This is, of course. an extreme instance.
 
 onstrated that because structure withstands large quiescent load that fact is little proof of stability under re- peated shocks and vibrations. Metals are believed to have life A bar, for example, may stand a million vibra- tions and break down at the million and first, and yet the last shock may be lighter than preceding ones. Attempts, however, to reduce this law to practical application have elicited an abundance of conflicting evidence; but, nevertheless, it is well settled that in no department of mechanics is an extended course of actual experiment. ing more urgently needed or of graver public importance"
 The strength of the Fay bridge at the time of its building was such that it was pronounced perhaps the most remarkable structure in the world Engineering, British magazine, speak ing of its test, when five engines, weighing S60 tons, were placed on g single span, said: 1.-The result is the complete establishment of this fact (sc important to the public), that the bridge is strong out of all proportion tc its possible necessities. The load which the structure is calculated to carry i: six times greater than that to which il was subjected"
 And yet thls great bridge, which cos $1,750,0O0, collapsed within few months after it was finished, the acci dent being the only one fn all railroad history in which no survivor lived to tel the tale.
 The theory of specialization put for ward at the time of the Ashtabxl; bridge disaster is now accepted as ac counting for many railroad accidents and seems peculiarly applicable to thu fall of the Bussey bridge. Vibration oOd Lo,,,o,o, bl ox,,o x.vor,1d coo,,, to bou.